Glass substrates including uniform parting agent coatings and methods of ceramming the same

ABSTRACT

Glass stack configurations including a carrier plate, setter plates, and glass sheets for thermal treatment of the glass sheets to form glass ceramic articles are provided. The glass stacking configurations and components described herein are selected to improve thermal uniformity throughout a glass stack during ceramming processes while maintaining or even reducing the stresses in the resultant glass ceramic article. Accordingly, the glass ceramic articles made according to the various embodiments described herein exhibit improved optical qualities and less warp than glass ceramic articles made according to conventional processes. Various embodiments of carrier plates, setter plates, parting agent compositions, and methods of stacking glass sheets are described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 119 ofU.S. Provisional Application Ser. No. 62/698,595 filed on Jul. 16, 2018and U.S. Provisional Application Ser. No. 62/749,800 filed on Oct. 24,2018, the contents of each of which are relied upon and incorporatedherein by reference in their entireties.

BACKGROUND Field

The present specification generally relates to methods and apparatus forceramming glass sheets and, more particularly, to parting agent coatingsfor use in ceramming glass sheets.

Technical Background

Conventional ceram processes utilize ceramic and/or refractory materialsas setters. However, such materials are incapable of producing a glassceramic having an optical quality suitable for use in optical displays.Without being bound by theory, it is believed that the heat transfer andheat capacity limitations of the ceramic and/or refractory materials canwarp or produce a skin effect on the glass ceramic.

Warp may also be introduced during the manufacturing process due to thestacking of the glass sheets. In particular, warping may result from theglass sheets in a stack sticking to the other glass sheets and/or thesetter, thickness variations of the glass sheets throughout the stacks,and the load applied to the glass stack.

Accordingly, alternative methods and apparatus are needed that aresuitable for use in producing glass ceramic sheets having a high opticalquality and reduced warping.

SUMMARY

According to one embodiment, a coated glass article includes a glasssubstrate having a parting agent layer thereon. The parting agent layeris formed from an aqueous dispersion including boron nitride and acolloidal inorganic binding agent. In various embodiments, the coatedglass substrate has a percent transmission of from about 76% to about83% as measured in accordance with ASTM D1003 and/or a percent haze offrom about 25% to about 38% as measured in accordance with ASTM D1044.In other embodiments, the coated glass substrate has a transmissionmetric (*T) of from about 19 to about 31; a transmission metric (*T) offrom about 23 to about 27; a haze metric (*H) of from about 10 to about50; and/or a haze metric (*H) of from about 20 to about 40, wherein thetransmission metric (*T) is defined as ((% transmission/thickness)*gsm),and the haze metric (*H) is defined as ((% haze/gsm)/thickness).

According to another embodiment, a method of ceramming a plurality ofglass sheets includes spray coating an aqueous dispersion includingboron nitride and a colloidal inorganic binding agent onto at least oneof a setter plate and one or more of the plurality of glass sheets,positioning the plurality of glass sheets between at least two setterplates in a glass stack configuration, and exposing the glass stackconfiguration to a ceramming cycle sufficient to ceram the plurality ofglass sheets.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from that description or recognized by practicing theembodiments described herein, including the detailed description whichfollows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description describe various embodiments ofprinting compositions, methods of printing on substrates, and printedsubstrates and are intended to provide an overview or framework forunderstanding the nature and character of the claimed subject matter.The accompanying drawings are included to provide a furtherunderstanding of the various embodiments, and are incorporated into andconstitute a part of this specification. The drawings illustrate thevarious embodiments described herein, and together with the descriptionserve to explain the principles and operations of the claimed subjectmatter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a glass stack configuration inaccordance with one or more embodiments described herein;

FIG. 2 is a graph showing the average and maximum stress (y-axis; MPa)in glass ceramic articles for various quench starting temperatures(x-axis);

FIG. 3 is a schematic illustration of a carrier plate having an opengrid configuration in accordance with one or more embodiments describedherein;

FIG. 4 is a schematic illustration of a carrier plate having a hollowplate configuration in accordance with one or more embodiments describedherein;

FIG. 5 is a graph plotting the modeled ΔT (° C.; y-axis) as a functionof heating time (minutes; x-axis) for an open grid steel carrier plateand a silicon carbide hollow carrier plate in accordance with one ormore embodiments described herein;

FIG. 6 is a graph plotting the modeled ΔT (° C.; y-axis) as a functionof heating time (minutes; x-axis) for the setter plates of Example A andComparative Examples 1 and 2;

FIG. 7 is a graph plotting the maximum stress (MPa; y-axis) for twodifferent setter materials in which reaction bonded silicon carbide isused on the left and silicon refractory board is used on the right;

FIG. 8 depicts EDX (energy dispersive X-ray) showing the lack of Si onthe surface of reaction-bonded silicon carbide setter plates postceramming in accordance with one or more embodiments described herein;

FIG. 9 depicts the XRD (X-ray diffraction) of various glass ceramicarticles in accordance with one or more embodiments described herein;

FIG. 10 is a graph of the maximum warp (μm; y-axis) for various setterplate flatnesses and additional weight in accordance with one or moreembodiments described herein;

FIG. 11 is a schematic illustrating the scan pattern for the CMM(coordinate measuring machine) measurement of the flatness of setterplates in accordance with one or more embodiments described herein;

FIG. 12 is a graph illustrating the maximum warp (μm; left y-axis) asbars through the thickness of the glass stack for various amounts ofapplied force and the maximum stress (MPa; right y-axis) as a line graphfor the various amounts of applied force in accordance with one or moreembodiments described herein;

FIG. 13 is a graph illustrating the maximum warp (μm; y-axis) throughthe thickness of glass stacks having various thickness variability inaccordance with one or more embodiments described herein;

FIG. 14 is a graph illustrating the maximum warp (μm; y-axis) throughthe thickness of the glass stack for various setter plate flatnesses inaccordance with one or more embodiments described herein;

FIG. 15A is a graphical representation of the warp of a 265 mm glassstrip with the edge bead removed in accordance with one or moreembodiments described herein;

FIG. 15B is a graphical representation of the warp of a 265 mm glassstrip with the edge bead remaining in accordance with one or moreembodiments described herein;

FIG. 16 is a graphical representation of the stress of a glass ceramicarticle with the edge bead remaining (top) and with the edge beadremoved (bottom) in accordance with one or more embodiments describedherein;

FIG. 17 is a graph plotting the critical delta T (° C.; y-axis) as afunction of part length (mm; x-axis) for glass ceramic parts of variouslengths and widths in accordance with one or more embodiments describedherein;

FIG. 18 is a graph of the % transmission (y-axis) for various glassstacks in accordance with one or more embodiments described herein;

FIG. 19 is a graph of the % haze (y-axis) for various glass stacks inaccordance with one or more embodiments described herein;

FIG. 20 is a graph plotting the maximum warp (μm; y-axis) as a functionof stack location (bottom of stack to top of stack from left to right;x-axis) for application of a parting agent coating using varying sprayhead spacings in accordance with one or more embodiments describedherein;

FIG. 21 is a schematic illustration of a glass stack configurationincluding interlayer setter plates in accordance with one or moreembodiments described herein;

FIG. 22 is a graph plotting the glass layer center temperature (° C.;y-axis) as a function of time (x-axis) for the top sheet of glass in aglass stack and the bottom sheet of glass in the glass stack inaccordance with one or more embodiments described herein;

FIG. 23 is a graph plotting the glass layer temperature (° C.; y-axis)as a function of time (x-axis) during a ceramming process for the topsheet of glass in a glass stack and the bottom sheet of glass in theglass stack in accordance with one or more embodiments described herein;and

FIG. 24 is a graph illustrating the maximum warp (μm; left y-axis) asbars through the thickness of the glass stack for various amounts ofapplied force and the maximum stress (MPa; right y-axis) as a line graphfor glass stacks without interlayer setter plates (left) and includinginterlayer setter plates (right) in accordance with one or moreembodiments described herein.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of methodsand apparatus for forming glass ceramic articles having improved opticalquality and reduced warping, examples of which are illustrated in theaccompanying drawings. Whenever possible, the same reference numeralswill be used throughout the drawings to refer to the same or like parts.

In general, described herein are glass stack configurations including acarrier plate, setter plates, and glass sheets for thermal treatment ofthe glass sheets to form glass ceramic articles. The glass stackingconfigurations and components described herein are selected to improvethermal uniformity throughout a glass stack during ceramming processeswhile maintaining or even reducing the stresses in the resultant glassceramic article. Accordingly, the glass ceramic articles made accordingto the various embodiments described herein exhibit improved opticalqualities and less warp than glass ceramic articles made according toconventional processes. Various embodiments of carrier plates, setterplates, parting agent compositions, and methods of stacking glass sheetswill be described herein with specific reference to the appendeddrawings.

Directional terms as used herein—for example up, down, right, left,front, back, top, bottom, vertical, horizontal—are made only withreference to the figures as drawn and are not intended to imply absoluteorientation unless otherwise expressly stated.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order, nor that with any apparatus specificorientations be required. Accordingly, where a method claim does notactually recite an order to be followed by its steps, or that anyapparatus claim does not actually recite an order or orientation toindividual components, or it is not otherwise specifically stated in theclaims or description that the steps are to be limited to a specificorder, or that a specific order or orientation to components of anapparatus is not recited, it is in no way intended that an order ororientation be inferred, in any respect. This holds for any possiblenon-express basis for interpretation, including: matters of logic withrespect to arrangement of steps, operational flow, order of components,or orientation of components; plain meaning derived from grammaticalorganization or punctuation; and the number or type of embodimentsdescribed in the specification.

As used herein, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. Thus, forexample, reference to “a” component includes aspects having two or moresuch components, unless the context clearly indicates otherwise.

In general, a process for forming a glass ceramic includes forming aglass article and ceramming the glass article to transform the glassarticle into a glass ceramic form. Referring to FIG. 1, an example stackconfiguration 100 for ceramming is illustrated. The stack configuration100 includes a carrier plate 102 supporting two setter plates 104, and aglass stack 106 positioned between the setter plates 104.

In some embodiments, insulation layers (not shown) may be located on thetop surface of the upper setter plate 104 and one the bottom surface ofthe lower setter plate 104. The insulation layers may be formed from anymaterial having a low thermal conductivity, and can reduce or eveneliminate axial temperature gradients of the glass sheets 108 on the topand bottom of the glass stack 106.

As shown in FIG. 1, the glass stack 106 includes a plurality of glasssheets 108, each glass sheet 108 being separated from an adjacent glasssheet 108 by a parting agent layer 110. As will be described in greaterdetail below, the parting agent layer 110 reduces or even eliminates thesticking of the glass sheets 108 in the glass stack 106 during theceramming process. Although not depicted in FIG. 1, in some embodiments,the glass stack 106 may further include a parting agent layer 110between the glass sheet 108 and the setter plate 104. In otherembodiments, such as in various embodiments described below, the setterplate 104 is made from a material that does not react with the glasssheet 108, and a parting agent layer 110 is not required to preventinteractions between the glass sheet 108 and the setter plate 104.

Generally, to form the glass ceramic, the glass stack 106 is heated at atemperature above its annealing point for a time sufficient to developcrystal nuclei (also called a nucleation phase). The heat treatment canbe performed, for example, in a lehr or furnace. After being heatedabove its annealing point, the glass is then further heated, usually ata higher temperature between the glass annealing point and the glasssoftening point, to develop the crystal phase (also called acrystallization phase). In various embodiments, the heat treatment, orceramming process, includes heating the glass stack to a nucleationtemperature, maintaining the nucleation temperature for a predeterminedperiod of time, heating the glass stack to a crystallizationtemperature, and maintaining the crystallization temperature for apredetermined period of time. In some embodiments, the step of heatingthe glass stack to a nucleation temperature can include heating theglass stack to a nucleation temperature of about 700° C. at a rate of1-10° C./min. The glass stack may be maintained at the nucleationtemperature for a time of from about ¼ hour to about 4 hours. The stepof heating the glass stack to the crystallization temperature caninclude heating the glass stack to a crystallization temperature ofabout 800° C. at a rate of 1-10° C./min. The glass stack may bemaintained at the nucleation temperature for a time of from about ¼ hourto about 4 hours.

However, it is contemplated that other heat treatment schedules(including varying times and/or temperatures) can be used, depending onthe particular embodiment. In particular, the temperature-temporalprofile of heat treatment steps are selected to produce one or more ofthe following attributes: crystalline phase(s) of the glass ceramic,proportions of one or more major crystalline phases and/or one or moreminor crystalline phases and residual glass, crystal phase assemblagesof one or more predominate crystalline phase and/or one or more minorcrystalline phases and residual glass, and grain sizes or grain sizedistributions among one or more major crystalline phases and/or one ormore minor crystalline phases, which in turn may influence the finalintegrity, quality, color and/or opacity of the resultant glass ceramicarticle.

Following heating to the nucleation temperature and maintaining thattemperature for the predetermined time, the glass stack is cooled backto room temperature. In various embodiments, the cooling rate iscontrolled down to a temperature of about 450° C., after which the glassceramic article may be quenched without impacting the stress, as shownin FIG. 2. Accordingly, in various embodiments, the ceramming processincludes a controlled cooling at a rate of about 4° C./min from themaximum temperature to a temperature of about 450° C., followed by aquenching step to bring the temperature to approximately roomtemperature.

Having described the stack configuration 100 in general, additionaldetail will now be provided with regard to the components of the stackconfiguration 100.

Carrier Plate

In various embodiments, the carrier plate 102 supports two or moresetter plates 104. The structure and material of the carrier plate 102may be selected to control the thermal uniformity of the glass sheetsloaded on top of it in the stack configuration 100. In some embodiments,the carrier plate 102 has an open carrier design (shown in FIG. 3),while in other embodiments, the carrier plate 102 has a closed carrierdesign (shown in FIG. 4). In the embodiment depicted in FIG. 3, thecarrier plate 102 is approximately 17% solid metal (e.g., steel), whilethe carrier plate 102 in the embodiment depicted in FIG. 4 is a hollowplate made of reaction bonded silicon carbide beams with approximately45% solid metal.

To evaluate the thermal impact of the carrier plate, a thermal modelassuming production scale capacity with 9 stacks and 23 glass sheets ineach stack on a carrier plate and 8 mm setter plates made from reactionbonded silicon carbide was run. As shown in the modeled data of FIG. 5,glass stacks on the hollow carrier plate exhibit reduced thermaluniformity as compared to glass stacks on the open steel carrier platedue to heat transfer. In particular, for the carrier made of siliconcarbide beams (FIG. 4), larger glass stack temperature variations areexpected as compared to the carrier made of the open steel grid design(FIG. 3), except at the very early stage of heating when the glasstemperatures are low. Additionally, the blocking of direct radiation bythe carrier plate also increases the overall heating time, despite thefact that the reaction bonded silicon carbide is a better heat conductorthan steel.

Accordingly, although various designs and materials may be employed forthe carrier plate 102, in various embodiments, the carrier plate is madefrom steel and has an open grid design, as depicted in FIG. 3.

Setter Plate

As shown in FIG. 1, in various embodiments, the carrier plate 102supports at least two setter plates 104. For example, although theembodiment shown in FIG. 1 includes a single glass stack 106 with asetter plate 104 above the glass stack 106 and a setter plate 104between the glass stack 106 and the carrier plate 102, it iscontemplated that additional setter plates 104 may be included, such asbeing positioned within the glass stack 106, and/or by positioningmultiple glass stacks 106 on the carrier plate 102, each glass stack 106having at least a setter plate 104 above the glass stack 106 and asetter plate 104 between the glass stack 106 and the carrier plate 102.

While most conventional ceram processes utilize ceramic and refractorymaterials to form setter plates, such materials have heat transfer andheat capacity limitations which make them unsuitable for producing ahigh optical quality that is desired or required for certainapplications. Additionally, setter plates made from such materials canexperience thermal expansion, oxidation, and creep, which can in turnlead to warp in the glass ceramic article.

Moreover, the setter plates 104 binding the glass stack 106 provide alateral heat transfer path to spread radiant heat from heating elements,which may lower the in-plane glass sheet temperature variations.Minimizing the temperature variations may in turn lead to a reduction inin-plane stresses and warp in the glass ceramic article. Accordingly, invarious embodiments, the setter plates 104 are selected to maximize thereduction in glass sheet temperature variation. In particular, thesetter plates 104 are selected to have a particular specific heatcapacity, density, and thermal diffusivity.

According to various embodiments, the setter plates have a specific heatcapacity (c_(p)) of from about 670 J/kg*K to about 850 J/kg*K, asmeasured in accordance with ASTM E1461 at room temperature. For example,the setter plates may have a specific heat capacity of from about 670J/kg*K to about 850 J/kg*K, from about 670 J/kg*K to about 800 J/kg*K,from about 670 J/kg*K to about 750 J/kg*K, or from about 670 J/kg*K toabout 700 J/kg*K, as measured in accordance with ASTM E1461 at roomtemperature and all ranges and subranges therebetween. Without beingbound by theory, it is believed that when the specific heat capacity isoutside of this range, the material is not able to give up heat andaccept heat at the appropriate rate which causes stress and warp in theglass in stacking configurations.

The setter plates in various embodiments additionally or alternativelymay be selected to have a bulk density of greater than about 2500 kg/m³,as measured in accordance with ASTM C20. For example, the setter platesmay have a bulk density of from about 2500 kg/m³ to about 4000 kg/m³,from about 2750 kg/m³ to about 3750 kg/m³, or from about 3000 kg/m³ toabout 3500 kg/m³, as measured in accordance with ASTM C20 and all rangesand subranges therebetween. Without being bound by theory, it isbelieved that materials having bulk densities in this range have lowporosity and do not significantly increase the weight in the stack. Abulk density that is too low can lead to material deterioration overtime and decreased life use of the material, whereas a bulk density thatis too high can lead to stress in the stack due to increased force onthe glass.

Moreover, in various embodiments, the setter plates have a thermaldiffusivity of greater than about 2.50×10⁻⁵ m²/s. For example, thesetter plates may have a thermal diffusivity of from about 2.50×10⁻⁵m²/s to about 5.50×10⁻⁴ m²/s, from about 3.0×10⁻⁵ m²/s to about5.00×10⁻⁴ m²/s from about 4.0×10⁻⁵ m²/s to about 4.50×10⁻⁴ m²/s, fromabout 4.50×10⁻⁵ m²/s to about 4.00×10⁻⁴ m²/s, from about 5.00×10⁻⁵ m²/sto about 3.50×10⁻⁴ m²/s, from about 5.50×10⁻⁵ m²/s to about 3.00×10⁻⁴m²/s, from about 6.00×10⁻⁵ m²/s to about 2.50×10⁻⁴ m²/s, from about6.50×10⁻⁵ m²/s to about 2.0×10⁻⁴ m²/s, from about 7.00×10⁻⁵ m²/s toabout 2.00×10⁻⁴ m²/s, or from about 7.50×10⁻⁵ m²/s to about 1.50×10⁻⁴m²/s and all ranges and subranges therebetween. Without being bound bytheory, if the thermal diffusivity is too low, the material will taketoo long to heat up and cool down causing thermal gradients in the stackwhich will lead to stress and warp. However, if the thermal diffusivityis too high, it could also lead to stress due to imparting thermalgradients in the stack. Glass sheets in contact with the setter plateswould be affected by heat transfer at different rates as opposed to theglass sheets in the center of the stack. Thermal diffusivity a can bedefined according to the following equation:

$\alpha = \frac{k}{\rho\; c_{p}}$

where k is thermal conductivity (W/m*K), ρ is density (kg/m³), and c_(p)is specific heat capacity (J/kg*K).

Accordingly, in various embodiments, the setter plates have a thermalconductivity (k) of greater than about 100 W/m-K, greater than about 125W/m-K, greater than about 150 W/m-K, greater than about 175 W/m-K, oreven greater than about 180 W/m-K, as measured in accordance with ASTME1461 at room temperature. For example, the setter plate may have athermal conductivity of from about 100 W/m-K to about 350 W/m-K, fromabout 125 W/m-K to about 325 W/m-K, from about 150 W/m-K to about 300W/m-K, from about 175 W/m-K to about 275 W/m-K, or from about 180 W/m-Kto about 250 W/m-K, as measured in accordance with ASTM E1461 at roomtemperature and all ranges and subranges therebetween. Without beingbound by theory, thermal conductivity too high or too low can inducethermal gradients in the stack leading to stress and warp.

Various materials having the desired specific heat capacity, density,and thermal diffusivity may be suitable for use in forming the setterplates described herein. One example material that is particularlysuitable for use is reaction bonded silicon carbide (SiSiC). Inembodiments, the setter plate 104 may comprise from about 85 wt % toabout 90 wt % reaction bonded silicon carbide. The setter plate 104 mayfurther comprise from about 10 wt % to about 15 wt % silicon metal (Si)and binding agents. Commercially available reaction bonded siliconcarbide products that may be suitable for use in forming the setterplate 104 can include, by way of example and not limitation, CRYSTAR RB™available from Saint-Gobain Ceramic Materials.

To confirm the impact of the thermal properties of the material used toform the setter plates, three different materials were used to formsetter plates having a thickness of 8 mm. In particular, Example A wasformed from reaction bonded silicon carbide, Comparative Example 1 wasformed using nitride bonded silicon carbide, and Comparative Example 2was formed using silicon refractory board. The thermal properties ofeach of these materials are provided in Table 1.

TABLE 1 Thermal Properties of Setter Plate Materials Nitride Reaction SiBonded Bonded Refractory SiC (SiSiC) Board Thermal 31 185 0.6Conductivity at room temperature (W/m*K) Bulk Density 2200 3030 2100(kg/m³) Specific Heat at 663 670 878 room temperature (J/kg*K) ThermalDiffusivity 2.13E−05 9.11E−05 3.25E−07 (m²/s)

The ΔT of the glass stack during heating ramp up was modeled. Theresults are shown in FIG. 6. In particular, as shown in FIG. 6, thereaction bonded silicon carbide exhibits a reduced heating time and areduced ΔT during the process. Comparative Example 2 using setter platesformed from silicon refractory board exhibited a significantly largertemperature variation, most likely because it is a poor heat conductor.However, the larger thermal diffusivity of Example A and ComparativeExample 1 (nitride bonded silicon carbide) showed more uniformtemperatures.

In addition to decreasing the temperature variation in the glass stack,the setter plate 104 of various embodiments is made from a material thatimparts lower stress as compared to conventional materials. For example,the thermal diffusivity of the reaction bonded silicon carbide impartslower stress in the glass ceramic article following ceramming heattreatment as compared to conventional setter plate materials. As shownin FIG. 7, the reaction bonded silicon carbide produced a lower maximumstress on the stacks (left hand side of the graph) as compared to stacksin contact with a silicon refractory board setter plate (right hand sideof the graph). Without being bound by theory, it is believed that thereduced temperature delta resulting from the thermal diffusivity of thereaction bonded silicon carbide reduces stress in the glass ceramicarticle as it grows crystals and phase transformation occurs in thearticle. The stress reduction directly impacts the warp in the glassceramic article. In particular, increased stresses induce higher warp inthe article, which can make it unusable for certain applications, suchas handheld electronic displays. However, the use of reaction bondedsilicon carbide reduces the stress in the glass ceramic article, therebyproviding low warp in the final product.

In various embodiments, the material used to form the setter plate 104is further selected based on its lack of reactivity with both thecarrier plate 102 and the glass ceramic article. Reaction bonded siliconcarbide is an example material that demonstrates low or even no reactionwith materials typically used to form the carrier plate 102. Inparticular, setter plates made from reaction bonded silicon carbide incontact with stainless steel alloy and Ni-based super alloy metalcarrier plates were tested up to 800° C. in air for 24 hour and for 100hours. As shown in FIG. 8, SEM (scanning electron microscope) and EDXexamination showed that there was no reaction of the metals with thereaction bonded silicon carbide. Specifically, the lack of Si found onthe carrier plate surfaces showed that there was no reaction with thefree Si in the reaction bonded silicon carbide microstructure.

Moreover, Li-based glass ceramics in contact with reaction bondedsilicon carbide material during a thermal ceramming process do notexhibit any skin effects, according to XRD phase assemblagecharacterization. For example, as shown in FIG. 9, the glass in contactwith the reaction bonded silicon carbide setter plate (A) is similar inphase to the bulk glass (B).

In addition to having improved thermal properties over other materials,reaction bonded silicon carbide has a low porosity (<1%), which canincrease the life of the setter plate during thermal cycling due toincreased resistance to oxidation, cracking, and reactivity throughdiffusion with other elements and materials.

In various embodiments, the setter plate 104 is also dimensioned toreduce warp in the glass ceramic article. In particular, the thicknessof the setter plate 104 and the flatness of the setter plate 104 arecontrolled to reduce both warp and stress in the glass ceramic.

During the ceramming process, the glass sheets 108 forming the glassstack 106, which is in contact with the setter plates 104, move andconform to the flatness of the setter plate 104. In various embodiments,the setter plate 104 may be machined to obtain particular flatness afterformation. As used herein, the term “flatness” refers to a tolerancezone defined by two parallel planes within which the surface lies. Forexample, a flatness of 100 micrometers (μm, microns) means that thesurface must lie entirely between two parallel planes that are at most100 μm apart. The impact of the flatness of the setter plate 104 on theflatness of the glass ceramic article is shown in FIG. 10. Specifically,as shown in FIG. 10, the maximum warp of the glass ceramic article isdecreased for setter plates having a flatness of 100 μm as compared tosetter plates having a flatness of 700 μm.

FIG. 10 further demonstrates that the use of additional weight (e.g.,double weight as used in Sample Set 1) does not significantly reducewarp. For example, for each of Sample Set 1, Sample Set 2, and SampleSet 3, the first five samples of each set were performed using a setterwith a flatness of 100 μm, while the last 5 samples of each set wereperformed using a setter with a flatness of 700 μm. The flatter setterreduced the warp to approximately the same amount independent of theweight, as shown by comparing Sample Set 1, which had double weight, toSample Sets 2 and 3, each of which have equalized weight.

In various embodiments, the setter plate 104 has a maximum flatness ofless than or equal to about 100 μm, less than or equal to about 75 μm,less than or equal to about 50 μm, less than or equal to about 45 μm,less than or equal to about 40 μm, less than or equal to about 35 μm,less than or equal to about 30 μm, or even less than or equal to about25 μm.

Flatness can be measured using a CMM and touch and/or non-touch probes.In various embodiments, the measurement density is 1 point/mm throughoutthe sweep trajectory and the measurement region is about 10 mm inboundfrom a side of the setter plate. The origin of alignment is at thecenter of the shorter edge, as shown in FIG. 11. To locate the origin,the CMM finds the corners of the setter plate 104 and calculates thedistance between the two corners. The origin is the distance divided bytwo. To determine the region of inspection, the probe is moved 10 mmhorizontally inbound from edge of the setter plate at the origin. Then,the probe is moved upwards about 325 mm to the start point. The sweepbegins at that point. Spacing between each line is about 15 mm, and thesetter plate is scanned in a serpentine pattern, as shown in FIG. 11.Flatness is evaluated by the CMM using the minimum zone method.

The thickness t of the setter plate 104 (shown in FIG. 1) is selected,at least in part, to balance the thermal effects of the setter plate 104on the glass stack 106 with inducement of warp. In particular, thethickness should be minimized for heat transfer and uniformity, yetmaximized for strength and warp resistance. Accordingly, in variousembodiments, the setter plate 104 has a thickness t of from about 6.5 mmto about 10 mm, or from about 7 mm to about 9.5 mm, or from about 7.5 mmto about 9 mm, or from about 7.9 mm to about 8.2 mm and all ranges andsubranges therebetween.

The density of the material used to form the setter plate 104 and thethickness of the setter plate 104 may further be selected based on theapplied force on the glass stack 106. FIG. 12 illustrates how additionalforce on the glass stack can contribute to increased stress in the glassceramic article. In particular, as shown in FIG. 12, the addition ofweight not only did not improve the warp (e.g., decrease the maximumwarp), but it further increased the maximum stress at various pointswithin the glass stack. Without being bound by theory, it is believedthat the addition of additional force constrains the glass sheets duringthe ceramming process when shrinkage occurs. Accordingly, it is believedthat the ability of the material to move freely during the cerammingprocess decreases warp in the glass ceramic article. In variousembodiments, setter plates 104 made from reaction bonded silicon carbidemay provide good heat transfer while maintaining low applied force,thereby resulting in low warp and stress in the glass ceramic article.

Glass Sheets

The glass sheets 108 may be made from any glass composition that issuitable for forming glass ceramic articles, although it should beunderstood that the glass composition of the glass sheets 108 can impactthe mechanical and optical properties of the glass ceramic article. Invarious embodiments, the glass composition is selected such that theresultant glass ceramic article has a petalite crystalline phase and alithium silicate crystalline phase and wherein the petalite crystallinephase and the lithium silicate crystalline phase have higher weightpercentages than other crystalline phases present in the glass ceramicarticle.

By way of example and not limitation, in various embodiments, the glasssheets 108 may be formed from a glass composition including from about55 wt % to about 80 wt % SiO₂, from about 2 wt % to about 20 wt % Al₂O₃,from about 5 wt % to about 20 wt % Li₂O, from about 0 wt % to about 10wt % B₂O₃, from about 0 wt % to about 5 wt % Na₂O, from about 0 wt % toabout 10 wt % ZnO, from about 0.5 wt % to about 6 wt % P₂O₅, and fromabout 0.2 wt % to about 15 wt % ZrO₂.

SiO₂, an oxide involved in the formation of glass, can function tostabilize the networking structure of glasses and glass ceramics. Invarious glass compositions, the concentration of SiO₂ should besufficiently high in order to form petalite crystal phase when the glasssheet is heat treated to convert to a glass ceramic. The amount of SiO₂may be limited to control the melting temperature of the glass, as themelting temperature of pure SiO₂ or high-SiO₂ glasses is undesirablyhigh. In some embodiments, the glass or glass ceramic compositioncomprises from about 55 wt % to about 80 wt % SiO₂. In some embodiments,the glass or glass ceramic composition comprises from about 69 wt % toabout 80 wt % SiO₂. In some embodiments, the glass or glass ceramiccomposition can comprise from about 55 wt % to about 80 wt %, about 55wt % to about 77 wt %, about 55 wt % to about 75 wt %, about 55 wt % toabout 73 wt %, about 60 wt % to about 80 wt %, about 60 wt % to about 77wt %, about 60 wt % to about 75 wt %, about 60 wt % to about 73 wt %,about 69 wt % to about 80 wt %, about 69 wt % to about 77 wt %, about 69wt % to about 75 wt %, about 69 wt % to about 73 wt %, about 70 wt % toabout 80 wt %, about 70 wt % to about 77 wt %, about 70 wt % to about 75wt %, about 70 wt % to about 73 wt %, about 73 wt % to about 80 wt %,about 73 wt % to about 77 wt %, about 73 wt % to about 75 wt %, about 75wt % to about 80 wt %, about 75 wt % to about 77 wt %, or about 77 wt %to about 80 wt % SiO₂.

Al₂O₃ may also provide stabilization to the network and also providesimproved mechanical properties and chemical durability. If the amount ofAl₂O₃ is too high, however, the fraction of lithium silicate crystalsmay be decreased, possibly to the extent that an interlocking structurecannot be formed. The amount of Al₂O₃ can be tailored to controlviscosity. Further, if the amount of Al₂O₃ is too high, the viscosity ofthe melt is also generally increased. In some embodiments, the glass orglass ceramic composition can comprise from about 2 wt % to about 20 wt% Al₂O₃. In some embodiments, the glass or glass ceramic composition cancomprise from about 6 wt % to about 9 wt % Al₂O₃. In some embodiments,the glass or glass ceramic composition can comprise from about 2 wt % toabout 20 wt %, about 2 wt % to about 18 wt %, about 2 wt % to about 15wt %, about 2 wt % to about 12 wt %, about 2 wt % to about 10 wt %,about 2 wt % to about 9 wt %, about 2 wt % to about 8 wt %, about 2 wt %to about 5 wt %, about 5 wt % to about 20 wt %, about 5 wt % to about 18wt %, about 5 wt % to about 15 wt %, about 5 wt % to about 12 wt %,about 5 wt % to about 10 wt %, about 5 wt % to about 9 wt %, about 5 wt% to about 8 wt %, 6 wt % to about 20 wt %, about 6 wt % to about 18 wt%, about 6 wt % to about 15 wt %, about 6 wt % to about 12 wt %, about 6wt % to about 10 wt %, about 6 wt % to about 9 wt %, 8 wt % to about 20wt %, about 8 wt % to about 18 wt %, about 8 wt % to about 15 wt %,about 8 wt % to about 12 wt %, about 8 wt % to about 10 wt %, 10 wt % toabout 20 wt %, about 10 wt % to about 18 wt %, about 10 wt % to about 15wt %, about 10 wt % to about 12 wt %, about 12 wt % to about 20 wt %,about 12 wt % to about 18 wt %, or about 12 wt % to about 15 wt % Al₂O₃.

In the glass and glass ceramics herein, Li₂O aids in forming bothpetalite and lithium silicate crystal phases. In fact, to obtainpetalite and lithium silicate as the predominant crystal phases, it isdesirable to have at least about 7 wt % Li₂O in the composition.Additionally, it has been found that once Li₂O gets too high (greaterthan about 15 wt %), the composition becomes very fluid. Accordingly, insome embodiments, the glass or glass ceramic composition can comprisefrom about 5 wt % to about 20 wt % Li₂O. In other embodiments, the glassor glass ceramic composition can comprise from about 10 wt % to about 14wt % Li₂O. In some embodiments, the glass or glass ceramic compositioncan comprise from about 5 wt % to about 20 wt %, about 5 wt % to about18 wt %, about 5 wt % to about 16 wt %, about 5 wt % to about 14 wt %,about 5 wt % to about 12 wt %, about 5 wt % to about 10 wt %, about 5 wt% to about 8 wt %, about 7 wt % to about 20 wt %, about 7 wt % to about18 wt %, about 7 wt % to about 16 wt %, about 7 wt % to about 14 wt %,about 7 wt % to about 12 wt %, about 7 wt % to about 10 wt %, about 10wt % to about 20 wt %, about 10 wt % to about 18 wt %, about 10 wt % toabout 16 wt %, about 10 wt % to about 14 wt %, about 10 wt % to about 12wt %, about 12 wt % to about 20 wt %, about 12 wt % to about 18 wt %,about 12 wt % to about 16 wt %, about 12 wt % to about 14 wt %, about 14wt % to about 20 wt %, about 14 wt % to about 18 wt %, about 14 wt % toabout 16 wt %, about 16 wt % to about 20 wt %, about 16 wt % to about 18wt %, or about 18 wt % to about 20 wt % Li₂O.

As noted above, Li₂O is generally useful for forming various glassceramics, but the other alkali oxides tend to decrease glass ceramicformation and form an aluminosilicate residual glass in the glassceramic. It has been found that more than about 5 wt % Na₂O or K₂O, orcombinations thereof, leads to an undesirable amount of residual glass,which can lead to deformation during crystallization and undesirablemicrostructures from a mechanical property perspective. The compositionof the residual glass may be tailored to control viscosity duringcrystallization, minimizing deformation or undesirable thermalexpansion, or control microstructure properties. Therefore, in general,the glass sheets may be made from glass compositions having low amountsof non-lithium alkali oxides. In some embodiments, the glass or glassceramic composition can comprise from about 0 wt % to about 5 wt % R₂O,wherein R is one or more of the alkali cations Na and K. In someembodiments, the glass or glass ceramic composition can comprise fromabout 1 wt % to about 3 wt % R₂O, wherein R is one or more of the alkalications Na and K. In some embodiments, the glass or glass ceramiccomposition can comprise from 0 wt % to about 5 wt %, 0 wt % to about 4wt %, 0 wt % to about 3 wt %, 0 wt % to about 2 wt %, 0 wt % to about 1wt %, >0 wt % to about 5 wt %, >0 wt % to about 4 wt %, >0 wt % to about3 wt %, >0 wt % to about 2 wt %, >0 wt % to about 1 wt %, about 1 wt %to about 5 wt %, about 1 wt % to about 4 wt %, about 1 wt % to about 3wt %, about 1 wt % to about 2 wt %, about 2 wt % to about 5 wt %, about2 wt % to about 4 wt %, about 2 wt % to about 3 wt %, about 3 wt % toabout 5 wt %, about 3 wt % to about 4 wt %, or about 4 wt % to about 5wt % Na₂O, K₂O, or combinations thereof.

The glass and glass ceramic compositions can include P₂O₅. P₂O₅ canfunction as a nucleating agent to produce bulk nucleation. If theconcentration of P₂O₅ is too low, the precursor glass does crystallize,but only at higher temperatures (due to a lower viscosity) and from thesurface inward, yielding a weak and often deformed body. However, if theconcentration of P₂O₅ is too high, the devitrification, upon coolingduring the formation of the glass sheets, can be difficult to control.Embodiments can include from >0 wt % to about 6 wt % P₂O₅. Otherembodiments can include from about 2 wt % to about 4 wt % P₂O₅. Stillother embodiments can include from about 1.5 wt % to about 2.5 wt %P₂O₅. In some embodiments, the glass or glass ceramic composition caninclude from 0 wt % to about 6 wt %, 0 wt % to about 5.5 wt %, 0 wt % to5 wt %, 0 wt % to about 4.5 wt %, 0 wt % to about 4 wt %, 0 wt % toabout 3.5 wt %, 0 wt % to about 3 wt %, 0 wt % to about 2.5 wt %, 0 wt %to about 2 wt %, 0 wt % to about 1.5 wt %, 0 wt % to about 1 wt %, >0 wt% to about 6 wt %, >0 wt % to about 5.5 wt %, >0 wt % to 5 wt %, >0 wt %to about 4.5 wt %, >0 wt % to about 4 wt %, >0 wt % to about 3.5 wt%, >0 wt % to about 3 wt %, >0 wt % to about >2.5 wt %, 0 wt % to about2 wt %, >0 wt % to about 1.5 wt %, >0 wt % to about 1 wt %, about 0.5 wt% to about 6 wt %, about 0.5 wt % to about 5.5 wt %, about 0.5 wt % to 5wt %, about 0.5 wt % to about 4.5 wt %, about 0.5 wt % to about 4 wt %,about 0.5 wt % to about 3.5 wt %, about 0.5 wt % to about 3 wt %, about0.5 wt % to about 2.5 wt %, about 0.5 wt % to about 2 wt %, about 0.5 wt% to about 1.5 wt %, about 0.5 wt % to about 1 wt %, about 1 wt % toabout 6 wt %, about 1 wt % to about 5.5 wt %, about 1 wt % to 5 wt %,about 1 wt % to about 4.5 wt %, about 1 wt % to about 4 wt %, about 1 wt% to about 3.5 wt %, about 1 wt % to about 3 wt %, about 1 wt % to about2.5 wt %, about 1 wt % to about 2 wt %, about 1 wt % to about 1.5 wt %,about 1.5 wt % to about 6 wt %, about 1.5 wt % to about 5.5 wt %, about1.5 wt % to 5 wt %, about 1.5 wt % to about 4.5 wt %, about 1.5 wt % toabout 4 wt %, about 1.5 wt % to about 3.5 wt %, about 1.5 wt % to about3 wt %, about 1.5 wt % to about 2.5 wt %, about 1.5 wt % to about 2 wt%, about 2 wt % to about 6 wt %, about 2 wt % to about 5.5 wt %, about 2wt % to 5 wt %, about 2 wt % to about 4.5 wt %, about 2 wt % to about 4wt %, about 2 wt % to about 3.5 wt %, about 2 wt % to about 3 wt %,about 2 wt % to about 2.5 wt %, about 2.5 wt % to about 6 wt %, about2.5 wt % to about 5.5 wt %, about 2.5 wt % to 5 wt %, about 2.5 wt % toabout 4.5 wt %, about 2.5 wt % to about 4 wt %, about 2.5 wt % to about3.5 wt %, about 2.5 wt % to about 3 wt %, about 3 wt % to about 6 wt %,about 3 wt % to about 5.5 wt %, about 3 wt % to 5 wt %, about 3 wt % toabout 4.5 wt %, about 3 wt % to about 4 wt %, about 3 wt % to about 3.5wt %, about 3.5 wt % to about 6 wt %, about 3.5 wt % to about 5.5 wt %,about 3.5 wt % to 5 wt %, about 3.5 wt % to about 4.5 wt %, about 3.5 wt% to about 4 wt %, about 4 wt % to about 6 wt %, about 4 wt % to about5.5 wt %, about 4 wt % to 5 wt %, about 4 wt % to about 4.5 wt %, about4.5 wt % to about 6 wt %, about 4.5 wt % to about 5.5 wt %, about 4.5 wt% to about 5 wt %, about 5 wt % to about 6 wt %, about 5 wt % to about5.5 wt %, or about 5.5 wt % to about 6 wt % P₂O₅.

In various glass and glass ceramic compositions, it is generally foundthat ZrO₂ can improve the stability of Li₂O—Al₂O₃—SiO₂—P₂O₅ glass bysignificantly reducing glass devitrification during forming and loweringliquidus temperature. At concentrations above 8 wt %, ZrSiO₄ can form aprimary liquidus phase at a high temperature, which significantly lowersliquidus viscosity. Transparent glasses can be formed when the glasscontains over 2 wt % ZrO₂. The addition of ZrO₂ can also help decreasethe petalite grain size, which aids in the formation of a transparentglass ceramic. In some embodiments, the glass or glass ceramiccomposition can comprise from about 0.2 wt % to about 15 wt % ZrO₂. Insome embodiments, the glass or glass ceramic composition can includefrom about 2 wt % to about 4 wt % ZrO₂. In some embodiments, the glassor glass ceramic composition can comprise from about 0.2 wt % to about15 wt %, about 0.2 wt % to about 12 wt %, about 0.2 wt % to about 10 wt%, about 0.2 wt % to about 8 wt %, about 0.2 wt % to about 6 wt %, about0.2 wt % to about 4 wt %, about 0.5 wt % to about 15 wt %, about 0.5 wt% to about 12 wt %, about 0.5 wt % to about 10 wt %, about 0.5 wt % toabout 8 wt %, about 0.5 wt % to about 6 wt %, about 0.5 wt % to about 4wt %, about 1 wt % to about 15 wt %, about 1 wt % to about 12 wt %,about 1 wt % to about 10 wt %, about 1 wt % to about 8 wt %, about 1 wt% to about 6 wt %, about 1 wt % to about 4 wt %, about 2 wt % to about15 wt %, about 2 wt % to about 12 wt %, about 2 wt % to about 10 wt %,about 2 wt % to about 8 wt %, about 2 wt % to about 6 wt %, about 2 wt %to about 4 wt %, about 3 wt % to about 15 wt %, about 3 wt % to about 12wt %, about 3 wt % to about 10 wt %, about 3 wt % to about 8 wt %, about3 wt % to about 6 wt %, about 3 wt % to about 4 wt %, about 4 wt % toabout 15 wt %, about 4 wt % to about 12 wt %, about 4 wt % to about 10wt %, about 4 wt % to about 8 wt %, about 4 wt % to about 6 wt %, about8 wt % to about 15 wt %, about 8 wt % to about 12 wt %, about 8 wt % toabout 10 wt %, about 10 wt % to about 15 wt %, about 10 wt % to about 12wt %, or about 12 wt % to about 15 wt % ZrO₂.

B₂O₃ is conducive to providing a glass sheet with a low meltingtemperature. Furthermore, the addition of B₂O₃ in the glass sheet andthus the glass ceramic article helps achieve an interlocking crystalmicrostructure and can also improve the damage resistance of the glassceramic article. When boron in the residual glass is not charge balancedby alkali oxides or divalent cation oxides, it will be intrigonal-coordination state (or three-coordinated boron), which opens upthe structure of the glass. The network around these three coordinatedboron is not as rigid as tetrahedrally coordinated (or four-coordinated)boron. Without being bound by theory, it is believed that glass sheetsand glass ceramics that include three-coordinated boron can toleratesome degree of deformation before crack formation. By tolerating somedeformation, the Vickers indentation crack initiation values areincreased. Fracture toughness of the glass sheets and glass ceramicsthat include three-coordinated boron may also be increased. Withoutbeing bound by theory, it is believed that the presence of boron in theresidual glass of the glass ceramic (and glass sheet) lowers theviscosity of the residual glass (or glass sheet), which facilitates thegrowth of lithium silicate crystals, especially large crystals having ahigh aspect ratio. A greater amount of three-coordinated boron (inrelation to four-coordinated boron) is believed to result in glassceramics that exhibit a greater Vickers indentation crack imitationload. In some embodiments, the amount of three-coordinated boron (as apercent of total B₂O₃) may be about 40% or greater, 50% or greater, 75%or greater, 85% or greater, or even 95% or greater. The amount of boronin general should be controlled to maintain chemical durability andmechanical strength of the cerammed bulk glass ceramic.

In one or more embodiments, the glass or glass ceramic compositioncomprises from 0 wt % to about 10 wt % or from 0 wt % to about 2 wt %B₂O₃. In some embodiments, the glass or glass ceramic composition cancomprise from 0 wt % to about 10 wt %, 0 wt % to about 9 wt %, 0 wt % toabout 8 wt %, 0 wt % to about 7 wt %, 0 wt % to about 6 wt %, 0 wt % toabout 5 wt %, 0 wt % to about 4 wt %, 0 wt % to about 3 wt %, 0 wt % toabout 2 wt %, 0 wt % to about 1 wt %, >0 wt % to about 10 wt %, >0 wt %to about 9 wt %, >0 wt % to about 8 wt %, >0 wt % to about 7 wt %, >0 wt% to about 6 wt %, >0 wt % to about 5 wt %, >0 wt % to about 4 wt %, >0wt % to about 3 wt %, >0 wt % to about 2 wt %, >0 wt % to about 1 wt %,about 1 wt % to about 10 wt %, about 1 wt % to about 8 wt %, about 1 wt% to about 6 wt %, about 1 wt % to about 5 wt %, about 1 wt % to about 4wt %, about 1 wt % to about 2 wt %, about 2 wt % to about 10 wt %, about2 wt % to about 8 wt %, about 2 wt % to about 6 wt %, about 2 wt % toabout 4 wt %, about 3 wt % to about 10 wt %, about 3 wt % to about 8 wt%, about 3 wt % to about 6 wt %, about 3 wt % to about 4 wt %, about 4wt % to about 5 wt %, about 5 wt % to about 8 wt %, about 5 wt % toabout 7.5 wt %, about 5 wt % to about 6 wt %, or about 5 wt % to about5.5 wt % B₂O₃.

MgO can enter petalite crystals in a partial solid solution. In one ormore embodiments, the glass or glass ceramic composition can comprisefrom 0 wt % to about 8 wt % MgO. In some embodiments, the glass or glassceramic composition can comprise from 0 wt % to about 8 wt %, 0 wt % toabout 7 wt %, 0 wt % to about 6 wt %, 0 wt % to about 5 wt %, 0 wt % toabout 4 wt %, 0 wt % to about 3 wt %, 0 wt % to about 2 wt %, 0 wt % toabout 1 wt %, about 1 wt % to about 8 wt %, about 1 wt % to about 7 wt%, about 1 wt % to about 6 wt %, about 1 wt % to about 5 wt %, about 1wt % to about 4 wt %, about 1 wt % to about 3 wt %, about 1 wt % toabout 2 wt %, about 2 wt % to about 8 wt %, about 2 wt % to about 7 wt%, about 2 wt % to about 6 wt %, about 2 wt % to about 5 wt %, about 2wt % to about 4 wt %, about 2 wt % to about 3 wt %, about 3 wt % toabout 8 wt %, about 3 wt % to about 7 wt %, about 3 wt % to about 6 wt%, about 3 wt % to about 5 wt %, about 3 wt % to about 4 wt %, about 4wt % to about 8 wt %, about 4 wt % to about 7 wt %, about 4 wt % toabout 6 wt %, about 4 wt % to about 5 wt %, about 5 wt % to about 8 wt%, about 5 wt % to about 7 wt %, about 5 wt % to about 6 wt %, about 6wt % to about 8 wt %, about 6 wt % to about 7 wt %, or about 7 wt % toabout 8 wt % MgO.

ZnO can enter petalite crystals in a partial solid solution. In one ormore embodiments, the glass or glass ceramic composition can comprisefrom 0 wt % to about 10 wt % ZnO. In some embodiments, the glass orglass ceramic composition can comprise from 0 wt % to about 10 wt %, 0wt % to about 9 wt %, 0 wt % to about 8 wt %, 0 wt % to about 7 wt %, 0wt % to about 6 wt %, 0 wt % to about 5 wt %, 0 wt % to about 4 wt %, 0wt % to about 3 wt %, 0 wt % to about 2 wt %, 0 wt % to about 1 wt %,about 1 wt % to about 10 wt %, about 1 wt % to about 9 wt %, about 1 wt% to about 8 wt %, about 1 wt % to about 7 wt %, about 1 wt % to about 6wt %, about 1 wt % to about 5 wt %, about 1 wt % to about 4 wt %, about1 wt % to about 3 wt %, about 1 wt % to about 2 wt %, about 2 wt % toabout 10 wt %, about 2 wt % to about 9 wt %, about 2 wt % to about 8 wt%, about 2 wt % to about 7 wt %, about 2 wt % to about 6 wt %, about 2wt % to about 5 wt %, about 2 wt % to about 4 wt %, about 2 wt % toabout 3 wt %, about 3 wt % to about 10 wt %, about 3 wt % to about 9 wt%, about 3 wt % to about 8 wt %, about 3 wt % to about 7 wt %, about 3wt % to about 6 wt %, about 3 wt % to about 5 wt %, about 3 wt % toabout 4 wt %, about 4 wt % to about 10 wt %, about 4 wt % to about 9 wt%, about 4 wt % to about 8 wt %, about 4 wt % to about 7 wt %, about 4wt % to about 6 wt %, about 4 wt % to about 5 wt %, about 5 wt % toabout 10 wt %, about 5 wt % to about 9 wt %, about 5 wt % to about 8 wt%, about 5 wt % to about 7 wt %, about 5 wt % to about 6 wt %, about 6wt % to about 10 wt %, about 6 wt % to about 9 wt %, about 6 wt % toabout 8 wt %, about 6 wt % to about 7 wt %, about 7 wt % to about 10 wt%, about 7 wt % to about 9 wt %, about 7 wt % to about 8 wt %, about 8wt % to about 10 wt %, about 8 wt % to about 9 wt %, or about 9 wt % toabout 10 wt % ZnO.

In various embodiments, the glass or glass ceramic composition mayfurther include one or more constituents, such as, by way of example andnot limitation, TiO₂, CeO₂, and SnO₂. Additionally or alternatively,antimicrobial components may be added to the glass or glass ceramiccomposition. Antimicrobial components that may be added to the glass orglass ceramic may include, but are not limited to, Ag, AgO, Cu, CuO,Cu₂O, and the like. In some embodiments, the glass or glass ceramiccomposition may further include a chemical fining agent. Such finingagents include, but are not limited to, SnO₂, As₂O₃, Sb₂O₃, F, Cl, andBr. Additional details on glass and/or glass ceramic compositionssuitable for use in various embodiments may be found in, for example,U.S. Patent Application Publication No. 2016/0102010 entitled “HighStrength Glass-Ceramics Having Petalite and Lithium SilicateStructures,” filed Oct. 8, 2015, which is incorporated by referenceherein in its entirety.

In various embodiments, the glass compositions can be manufactured intosheets via processes, including but not limited to, slot draw, float,rolling, and other sheet-forming processes known to those skilled in theart.

According to various embodiments herein, the thickness uniformity of theglass sheets 108 is controlled to decrease the warp of the glass ceramicarticle. In FIG. 13, the maximum warp for glass stacks of 10 glasssheets and 24 glass sheets for both as-rolled glass and lapped glass isshown. As shown in FIG. 13, for glass stacks including as-rolled glasssheets with a maximum thickness variation of 64 μm, the maximum warp wassignificantly increased as compared to glass stacks including lappedglass sheets with a maximum thickness variation of 21 μm. Additionally,as demonstrated by the data in FIG. 14, the flatness of the setter plate104 (as described above) has an impact that is limited by thevariability of the thickness of the glass sheets. In particular, FIG. 14shows that for a 10 glass sheet stack configuration of as-rolled glass,a 78 μm reduction in the flatness of the setter plate has a limitedimpact on the warp of the glass ceramic article. Accordingly, followingsheet formation, in various embodiments, the glass sheets may bemachined or otherwise processed to reduce the thickness variability ofthe glass sheets.

In various embodiments, the edge bead may be removed from glass sheetsto decrease the amount of warp observed in the glass ceramic article. Itis believed that the edge beads have higher thickness non-uniformity andtherefore contribute to warp during the ceramming process. Inparticular, in embodiments in which a single sheet of glass is subjectedto the ceramming process (e.g., not incorporated into a glass stack),the removal of the edge bead can reduce warp in the glass sheet. Asshown in FIG. 15A, the removal of the edge bead (approximately 10 mm oneach side of the glass sheet) decreases the maximum flatness by 56 μm ascompared to the glass sheet without removal of the edge bead (FIG. 15B).Additionally, as shown in FIG. 16, the stress in the glass ceramicarticle is reduced when the bead is removed (bottom) as compared to whenthe glass ceramic article is cerammed including the bead (top). However,unexpectedly, removal of the edge bead from glass sheets incorporatedinto a glass stack during the ceramming process results in increasedwarp in embodiments in which a parting agent layer is not alsoincorporated into the glass stack. Without being bound by theory, it isbelieved that the increase in surface area contact resulting from theremoval of the edge beads of adjacent glass sheets provides additionalarea for sticking to occur. Accordingly, in embodiments in which theedge bead is removed and the glass sheet is to be incorporated into aglass stack, a parting agent layer is incorporated.

In various embodiments, part size is also taken into account to controlwarp and stress in the glass ceramic article. As shown in FIG. 17, thecritical ΔT decreases with part size. In particular, the critical ΔT isthe ΔT at which stress and warp may be induced for various part lengthsand widths. Accordingly, for larger parts, a larger ΔT may be acceptablewithout inducing warp or buckling into the final glass ceramic article.

Accordingly, in various embodiments, the thickness variation of theglass sheets can be controlled individually and throughout the glassstack, such as by edge bead removal and lapping, to reduce the warp andstress imparted to the glass ceramic article.

Parting Agent Layer

As described hereinabove, in various embodiments, a parting agent layer110 is deposited between adjacent glass sheets 108 in the glass stack106. In some embodiments, a parting agent layer 110 may also bedeposited between the setter plate 104 and the glass stack 106. Forexample, a parting agent layer 110 may be coated onto the setter plate104, or may be deposited on the surface of the glass sheet 108 at thetop and/or bottom of the glass stack 106.

In various embodiments, the parting agent layer 110 is formed from aparting agent composition which comprises an aqueous dispersionincluding boron nitride and a colloidal inorganic binding agent. Inembodiments, the parting agent composition is substantially free ofvolatile organic solvents. Accordingly, processes employing the partingagent composition may generate less hazardous waste than conventionalprocesses using alcohol-based products.

According to various embodiments, the parting agent composition includesboron nitride as a lubricant. The use of boron nitride enables theparting agent composition to be used in high temperatures (e.g., >500°C.) applications, which may not be possible with alternative lubricants.Additionally, boron nitride may be particularly well-suited for use as alubricant in various embodiments because it maintains its lubricationproperties throughout the ceramming process. In the parting agentcomposition of various embodiments, the boron nitride is present in theform of agglomerated particles having an average particle size of lessthan or equal to about 20 microns, for example, 90% of the agglomeratedparticles have an average particle size of less than 20 microns; 50% ofthe agglomerated particles have an average particle size of less than 10microns; 10% of the agglomerated particles have an average particle sizeof less than 5 microns; 90% of the agglomerated particles have anaverage particle size of less than 18.5 microns; 50% of the agglomeratedparticles have an average particle size of less than 6.5 microns; 10% ofthe agglomerated particles have an average particle size of less than3.5 microns; or an average particle size of from about 2 μm to about 4μm in the slurry. Although the particle size may vary depending on theparticular embodiment employed, the particle size generally should notexceed about 20 μm to reduce surface roughness and enable the formationof ultra-thin (e.g., 0.1 grains per square meter (gsm) dry weight, or0.5 gsm, or 1.0 gsm, or 1.5 gsm, or 2 gsm, or 2.5 gsm, or 3 gsm) coatinglayers.

As described above, the parting agent composition further includes acolloidal inorganic binding agent. The colloidal inorganic binding agentmay include, by way of example and not limitation, aluminum oxide(AlOx). Other colloidal inorganic binding agents may be used, providedthat they do not fully decompose during the heat treatment (e.g.,ceramming) process.

In some embodiments, the parting agent composition may optionallyinclude one or more dispersants or other additives. For example,antimicrobial additives may be employed. Suitable dispersants includenitric acid or other dispersants known and used in the art. However, inother embodiments, the parting agent composition may be substantiallyfree of additional components in order to reduce the likelihood ofreaction between the parting agent layer 110 and the glass sheets 108and/or the setter plate 104.

The parting agent composition has a specific gravity of from about 1.0to about 1.2 as measured using a syringe to pull off a predeterminedvolume of the parting agent composition and weighing that volume.Specifically, to measure the specific gravity, a 20 mL syringe is usedto pull about 10 mL of the parting agent composition into the syringeand pushed back out to evacuate bubbles. The syringe is then wipedclean, placed on a scale, and the scale is zeroed out. Then, exactly 20mL of the parting agent composition is pulled into the syringe, thesyringe is wiped clean, and placed on the scale to get the weight ingrams in the syringe. The weight is then divided by 20 to get thespecific gravity.

Additionally or alternatively, in various embodiments, the parting agentcomposition has a viscosity of from about 120 centipoise (cP) to about160 cP as measured on a Brookfield DV2TLV Viscometer, four spindle andall ranges and subranges therebetween. Although the viscosity may varydepending on the particular embodiment, a viscosity greater than 160 cPor less than 120 cP may adversely impact the application of thecomposition to the glass sheets, and may result in an uneven partingagent layer.

In various embodiments, the parting agent composition has a pH of fromabout 3 to about 5 and all ranges and subranges therebetween. Inparticular, when the parting agent composition has a pH in this range,the composition is compatible with application to the surface of theglass sheet without concern for pitting or etching the surface. Suitablecommercially available parting agents include those available from ZypCoatings (Tennessee).

As described above, the parting agent composition may be applied to oneor more surfaces of the glass sheets 108 and/or the setter plates 104 toform a parting agent layer 110. In various embodiments, the partingagent composition is applied via a spray dispersion technique, such asrotary atomization and/or air assisted spray dispersion. Without beingbound by theory, it is believed that other application techniques,including but not limited to roller coating, dipping, and ultrasonicpowder application, are unable to achieve the desired layer thicknessand uniformity desired by various embodiments. Accordingly, in variousembodiments, the parting agent composition is dried to form a partingagent layer 110 having a dry coat weight of from about 0.1 gsm to about6 gsm (for example about 0.5 gsm, or about 1.0 gsm, or about 1.5 gsm, orabout 2 gsm, or about 2.5 gsm, or about 3 gsm, or about 3.5 gsm, orabout 4 gsm, or about 4.5 gsm, or about 5.0 gsm, or about 5.5 gsm, andall ranges and subranges therebetween, for example about 0.1 gsm toabout 6 gsm, or about 0.1 gsm to about 5 gsm, or about 0.1 gsm to about4 gsm, or about 0.1 gsm to about 3 gsm, or about 0.2 gsm to about 3 gsm,or about 0.3 gsm to about 3 gsm, or about 0.4 gsm to about 3 gsm, orabout 0.5 gsm to about 3 gsm). Although the thickness of the partingagent layer 110 can vary depending on the particular embodiment, it isgenerally expected that dry coat weights of less than about 2 gsm (forexample less than about 1.5 gsm, or less than about 1.0 gsm, or lessthan about 0.5 gsm, or less than about 0.4 gsm, or less than about 0.3gsm, or less than about 0.2 gsm, or less than about 0.1 gsm) may have anincreased risk of sticking. Additionally, in various embodiments, theparting agent layer 110 has a substantially uniform distribution on thesurface of the glass sheet 108 and/or the setter plate 104.

In embodiments described herein, coating uniformity was characterized bypercent haze and percent transmittance using a BYK Haze-Gard Plusinstrument from the Paul N. Gardner Company, Inc. in accordance withASTM D 1003 (for transmission) and ASTM D 1044 (for haze). The Haze-GardPlus is capable of directly determining total transmittance, haze andclarity. The instrument utilizes an Illuminant C light sourcerepresenting average day light with a correlated color temperature of6774 K. In various embodiments, the cerammed glass sheet 100 having aparting agent layer 110 on one surface thereof has a percenttransmission of from about 76% to about 83% as measured in accordancewith ASTM D1003 and a percent haze of from about 25% to about 38% asmeasured in accordance with ASTM D1044. In some embodiments, becausetransmission and/or haze may be dependent upon coating thickness, thecerammed sheet having a parting agent layer on one surface thereof has atransmission metric (*T) of from about 19 to about 31; a transmissionmetric (*T) of from about 23 to about 27; a haze metric (*H) of fromabout 10 to about 50; and/or a haze metric (*H) of from about 20 toabout 40.

FIG. 18 is a plot of the percent transmission (y-axis) versusacceptability of the samples (x-axis). In particular, the percenttransmission is shown for Li-based glass ceramic articles including aparting agent layer. As shown in FIG. 18, a coating that is too thick(e.g., greater than about 3.0 gsm, or greater than about 3.5 gsm, orgreater than about 4.0 gsm, or greater than about 4.5 gsm, or greaterthan about 5.0 gsm, or greater than about 5.5 gsm, or greater than about6 gsm) exhibits a percent transmission of less than 70% (in theseexamples a transmission metric (*T) outside of from about 19 to about31, or a transmission metric (*T) outside of from about 23 to about 27),while a coating that is too thin (e.g., less than about 2 gsm, forexample less than about 1.5 gsm, or less than about 1.0 gsm, or lessthan about 0.5 gsm, or less than about 0.4 gsm, or less than about 0.3gsm, or less than about 0.2 gsm, or less than about 0.1 gsm) exhibits apercent transmission of about 85% (in these examples a transmissionmetric (*T) outside of from about 19 to about 31 or a transmissionmetric (*T) outside of from about 23 to about 27), but the glass sticksto adjacent glass sheets. However, samples that were otherwiseacceptable exhibited a percent transmission of from about 76% to about83% as measured in accordance with ASTM D1003, or a transmission metric(*T) of from about 19 to about 31, or a transmission metric (*T) of fromabout 23 to about 27.

FIG. 19 is a plot of the percent haze (y-axis) versus the acceptabilityof the samples (x-axis). For samples having a coating that was too thick(e.g., greater than about 3.0 gsm, or greater than about 3.5 gsm, orgreater than about 4.0 gsm, or greater than about 4.5 gsm, or greaterthan about 5.0 gsm, or greater than about 5.5 gsm, or greater than about6 gsm), the percent haze was greater than about 40% (in these examples ahaze metric (*H) outside of from about 10 to about 50, or a haze metric(*H) outside of from about 20 to about 40), while samples that hadcoatings that were too thin (e.g., less than about 2 gsm, for exampleless than about 1.5 gsm, or less than about 1.0 gsm, or less than about0.5 gsm, or less than about 0.4 gsm, or less than about 0.3 gsm, or lessthan about 0.2 gsm, or less than about 0.1 gsm), the percent haze wasless than about 25% (in these examples a haze metric (*H) outside offrom about 10 to about 50, or a haze metric (*H) outside of from about20 to about 40) and the samples exhibited sticking. However, samplesthat were otherwise acceptable exhibited a percent haze of from about25% to about 38% as measured in accordance with ASTM D1044 (in theseexamples a haze metric (*H) of from about 10 to about 50, or a hazemetric (*H) of from about 20 to about 40).

In various embodiments, glass ceramic articles including the partingagent layer 110 exhibit less warp than glass ceramic articles formedwithout the parting agent layer 110. In other words, in addition toreducing the sticking between a glass sheet 108 and an adjacent glasssheet 108 and/or the setter plate 104, the parting agent layer 110 canreduce warp in the final glass ceramic article. Without being bound bytheory, it is believed that application of a parting agent layer 110 asdescribed herein can prevent localized sticking which contributes towarp in the glass ceramic article. In particular, during the cerammingprocess, the glass experiences shrinkage during phase change and crystalgrowth and the presence of the parting agent layer 110 allows the glassto move freely without constraint in the glass stack 106.

FIG. 20 is a graph of the maximum warp (in μm; y-axis) as a function ofglass stack location (x-axis). The coating was applied with a 1.5″ sprayhead spacing (solid line) and a 3.0″ spray head spacing (dotted line).FIG. 20 shows that maximum warp increases from the bottom of the glassstack (left) to the top of the glass stack (right). Additionally, inembodiments in which the coating was applied with slight variances inthe thickness and uniformity of the coating layer (3.0″ spray headspacing), the max warp increases over the entire thickness of the glassstack as compared to a uniform application of the coating layer at drycoat weight of about 2 gsm with a 1.5″ spray head spacing. Thus,demonstrated by the data presented in FIG. 20, sticking causes loweryields and physical degradation of the glass ceramic article andlocalized stiction constrains the glass, which increases warp in thefinal product.

In addition to decreasing the warp of the glass ceramic article, theparting agent layer 110 of various embodiments described herein has beenfound to leave the phase assemblage of the glass ceramic articleunchanged. FIG. 9 is an XRD of the glass ceramic article including theparting agent layer 110 as cerammed (C) and post polishing (D). Thesurface layer effect is measured to be less than about 1 μm.

Thus, in various embodiments, the parting agent layer 110 can reduce CTEmismatch between the glass sheets 108 and the setter plate 104, reducescuffing, and extend the life of the setter plates 104 by reducing wear.For example, it is believed that the CTE mismatch between the glasssheets 108 and the setter plate 104 can lead to scuffing if the glasssheets 108 stick to the setter plate 104. However, various embodimentsof the parting agent composition, and particularly the colloidal binder,do not fully decompose during the thermal process. Accordingly, partingagent composition can be used to coat the setter plate 104 for multipleuses (e.g., greater than about 25 cycles) before the setter plate 104needs to be re-coated. Therefore, in various embodiments, the partingagent layer 110, when applied in as an ultra-thin and uniform layer,prevents sticking in high temperature glass-glass stackingconfigurations, which can, in turn, reduce warp of a final glass ceramicarticle.

Glass Stack Configuration

In various embodiments described herein, multiple glass sheets 108 arearranged in a glass stack 106 for the ceramming process. In addition tothe variables described above as impacting the warp and stress of thefinal glass ceramic article, it was further discovered that variouselements of the glass stacking configuration have an impact on the warpand stress of the glass ceramic article.

Accordingly, in various embodiments, interlayer setter plates 112 may beplaced within the glass stack 106, as shown in FIG. 21. The inclusion ofthe interlayer setter plates 112 can increase heat transfer and decreasethe temperature lag from the top of the glass stack to the bottom of theglass stack. As shown in FIG. 22, when the temperature of each glasssheet in the stack including three interlayer setter plates is measuredduring the nucleation stage of the ceramming process, there is a 2.2° C.variability between the top layer of the top stack and the bottom layerof the bottom stack. Moreover, as shown in FIG. 23, although thereremains a temperature differential during the ramping periods of theceramming process, the inclusion of interlayer setter plates in theglass stack achieves temperature uniformity throughout the glass stackduring the soaking periods.

Additionally, the inclusion of interlayer setter plates 112 reduces thewarp and does not significantly impact the stress in the glass ceramicarticle, as shown in FIG. 24. Specifically, FIG. 24 shows that theinclusion of the interlayer setter plates 112 (right side of the graph)can reset the additive warp at each interlayer setter plate as comparedto the increasing warp of the glass stack without interlayer setterplates (left side of the graph). The maximum stress is shown in FIG. 24as the line graph, which does not increase with the addition of theinterlayer setter plates.

In addition to including interlayer setter plates 112 within the glassstack 106, warp and stress in the glass ceramic article may further becontrolled or reduced by limiting the number of glass sheetsincorporated in the glass stack. For example, in some embodiments, theglass stack can be from 6 to 24 glass sheets, or from 10 to 20 glasssheets from setter plate 104 to setter plate 104. In embodiments inwhich interlayer setter plates are disposed within the glass stack, thenumber of glass sheets between each interlayer setter plate may be from5 glass sheets to 15 glass sheets, or from 6 glass sheets to 10 glasssheets.

Accordingly, various embodiments described herein may be employed toproduce glass ceramic articles having excellent optical quality andreduced warp while not adversely impacting, or even improving, stress inthe glass ceramic articles as compared to glass articles cerammedaccording to conventional techniques. Such glass ceramic articles may beparticularly well-suited for use in portable electronic devices due totheir strength performance and high transmission and/or hightransmission metric values.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the embodiments describedherein without departing from the spirit and scope of the claimedsubject matter. Thus it is intended that the specification cover themodifications and variations of the various embodiments described hereinprovided such modification and variations come within the scope of theappended claims and their equivalents. For example, the various featuresof the disclosure may be combined as per the following non-exhaustivelist of embodiments.

Embodiment 1

A coated glass article comprising:

a glass substrate having a parting agent layer thereon, the partingagent layer formed from an aqueous dispersion comprising boron nitrideand a colloidal inorganic binding agent.

Embodiment 2

The coated glass article according to Embodiment 1, wherein thecolloidal inorganic binding agent comprises aluminium oxide.

Embodiment 3

The coated glass article according to Embodiment 1 or Embodiment 2,wherein the boron nitride is present in the form of agglomeratedparticles having an average particle size at least one of: less than orequal to about 20 μm; wherein at least one of: 90% of the agglomeratedparticles have an average particle size of less than 20 microns; 50% ofthe agglomerated particles have an average particle size of less than 10microns; 10% of the agglomerated particles have an average particle sizeof less than 5 microns; 90% of the agglomerated particles have anaverage particle size of less than 18.5 microns; 50% of the agglomeratedparticles have an average particle size of less than 6.5 microns; or 10%of the agglomerated particles have an average particle size of less than3.5 microns.

Embodiment 4

The coated glass article according to any of the preceding Embodiments,wherein the aqueous dispersion is substantially free of volatile organicsolvents.

Embodiment 5

The coated glass article according to any of the preceding Embodiments,wherein the aqueous dispersion further comprises at least onedispersant.

Embodiment 6

The coated glass article according to any of the preceding Embodiments,wherein the parting agent layer has a dry coat weight of from about 0.1gsm to about 6 gsm.

Embodiment 7

The coated glass article according to any of the preceding Embodiments,wherein the glass substrate comprises a glass ceramic substrate.

Embodiment 8

The coated glass substrate according to Embodiment 7, wherein the coatedglass substrate has at least one of: a transmission metric (*T) of fromabout 19 to about 31; a transmission metric (*T) of from about 23 toabout 27; a haze metric (*H) of from about 10 to about 50; or a hazemetric (*H) of from about 20 to about 40.

Embodiment 9

The coated glass substrate according to Embodiment 7 or Embodiment 8,wherein the coated glass substrate has a surface layer effect of lessthan about 1 micron.

Embodiment 10

A method of ceramming a plurality of glass sheets comprising:

spray coating an aqueous dispersion comprising boron nitride and acolloidal inorganic binding agent onto at least one of a setter plateand one or more of the plurality of glass sheets;

positioning the plurality of glass sheets between at least two setterplates in a glass stack configuration; and

exposing the glass stack configuration to a ceramming cycle sufficientto ceram the plurality of glass sheets into glass-ceramic sheets.

Embodiment 11

The method according to Embodiment 10, wherein the colloidal inorganicbinding agent comprises aluminium oxide.

Embodiment 12

The method according to Embodiment 10 or Embodiment 11, wherein theboron nitride is present in the slurry the form of agglomeratedparticles wherein at least one of: 90% of the agglomerated particleshave an average particle size of less than 20 microns; 50% of theagglomerated particles have an average particle size of less than 10microns; 10% of the agglomerated particles have an average particle sizeof less than 5 microns; 90% of the agglomerated particles have anaverage particle size of less than 18.5 microns; 50% of the agglomeratedparticles have an average particle size of less than 6.5 microns; or 10%of the agglomerated particles have an average particle size of less than3.5 microns.

Embodiment 13

The method according to any of Embodiments 10-12, wherein the aqueousdispersion is substantially free of volatile organic solvents.

Embodiment 14

The method according to any of Embodiments 10-13, wherein the aqueousdispersion has a specific gravity of from about 1.0 to about 1.2.

Embodiment 15

The method according to any of Embodiments 10-14, wherein the aqueousdispersion has a viscosity of from about 120 cP to about 160 cP.

Embodiment 16

The method according to any of Embodiments 10-15, wherein the aqueousdispersion has a pH of from about 3 to about 5.

Embodiment 17

The method according to any of Embodiments 10-16, wherein the aqueousdispersion is spray coated onto a surface of one of the plurality ofglass sheets to form a parting agent layer, and wherein positioning theplurality of glass sheets between the at least two setter platescomprises positioning the glass sheet having the parting agent layerthereon below an adjacent glass sheet such that the parting agent layeris between the surface of the glass sheet and the adjacent glass sheet.

Embodiment 18

The method according to Embodiment 17, wherein the parting agent layerhas a dry coat weight of from about 0.1 gsm to about 6 gsm.

Embodiment 19

The method according to Embodiment 17 or Embodiment 18, wherein, afterexposing the glass stack configuration to the ceramming cycle, the glasssheet having the parting agent layer thereon has at least one of: atransmission metric (*T) of from about 19 to about 31; a transmissionmetric (*T) of from about 23 to about 27; a haze metric (*H) of fromabout 10 to about 50; or a haze metric (*H) of from about 20 to about40.

Embodiment 20

The method according to any of Embodiments 17-19, wherein, afterexposing the glass stack configuration to the ceramming cycle, the glasssheet having the parting agent layer thereon has a surface layer effectof less than about 1 micron.

1. A coated glass article comprising: a glass substrate having a partingagent layer thereon, the parting agent layer formed from an aqueousdispersion comprising boron nitride and a colloidal inorganic bindingagent.
 2. The coated glass article according to claim 1, wherein thecolloidal inorganic binding agent comprises aluminium oxide.
 3. Thecoated glass article according to claim 1, wherein the boron nitride ispresent in the form of agglomerated particles having an average particlesize of at least one of: less than or equal to about 20 μm; wherein atleast one of: 90% of the agglomerated particles have an average particlesize of less than 20 microns; 50% of the agglomerated particles have anaverage particle size of less than 10 microns; 10% of the agglomeratedparticles have an average particle size of less than 5 microns; 90% ofthe agglomerated particles have an average particle size of less than18.5 microns; 50% of the agglomerated particles have an average particlesize of less than 6.5 microns; or 10% of the agglomerated particles havean average particle size of less than 3.5 microns.
 4. The coated glassarticle according to claim 1, wherein the aqueous dispersion issubstantially free of volatile organic solvents.
 5. The coated glassarticle according to claim 1, wherein the aqueous dispersion furthercomprises at least one dispersant.
 6. The coated glass article accordingto claim 1, wherein the parting agent layer has a dry coat weight offrom about 0.1 gsm to about 6 gsm.
 7. The coated glass article accordingto claim 1, wherein the glass substrate comprises a glass ceramicsubstrate.
 8. The coated glass substrate according to claim 7, whereinthe coated glass substrate has at least one of: a transmission metric(*T) of from about 19 to about 31; a transmission metric (*T) of fromabout 23 to about 27; a haze metric (*H) of from about 10 to about 50;or a haze metric (*H) of from about 20 to about
 40. 9. The coated glasssubstrate according to claim 7, wherein the coated glass substrate has asurface layer effect of less than about 1 micron.
 10. A method ofceramming a plurality of glass sheets comprising: spray coating anaqueous dispersion comprising boron nitride and a colloidal inorganicbinding agent onto at least one of a setter plate and one or more of theplurality of glass sheets; positioning the plurality of glass sheetsbetween at least two setter plates in a glass stack configuration; andexposing the glass stack configuration to a ceramming cycle sufficientto ceram the plurality of glass sheets into glass-ceramic sheets. 11.The method according to claim 10, wherein the colloidal inorganicbinding agent comprises aluminium oxide.
 12. The method according toclaim 10, wherein the boron nitride is present in the aqueous dispersionin the form of agglomerated particles wherein at least one of: 90% ofthe agglomerated particles have an average particle size of less than 20microns; 50% of the agglomerated particles have an average particle sizeof less than 10 microns; 10% of the agglomerated particles have anaverage particle size of less than 5 microns; 90% of the agglomeratedparticles have an average particle size of less than 18.5 microns; 50%of the agglomerated particles have an average particle size of less than6.5 microns; or 10% of the agglomerated particles have an averageparticle size of less than 3.5 microns.
 13. The method according toclaim 10, wherein the aqueous dispersion is substantially free ofvolatile organic solvents.
 14. The method according to claim 10, whereinthe aqueous dispersion has a specific gravity of from about 1.0 to about1.2.
 15. The method according to claim 10, wherein the aqueousdispersion has a viscosity of from about 120 cP to about 160 cP.
 16. Themethod according to claim 10, wherein the aqueous dispersion has a pH offrom about 3 to about
 5. 17. The method according to claim 10, whereinthe aqueous dispersion is spray coated onto a surface of one of theplurality of glass sheets to form a parting agent layer, and whereinpositioning the plurality of glass sheets between the at least twosetter plates comprises positioning the glass sheet having the partingagent layer thereon below an adjacent glass sheet such that the partingagent layer is between the surface of the glass sheet and the adjacentglass sheet.
 18. The method according to claim 17, wherein the partingagent layer has a dry coat weight of from about 0.1 gsm to about 6 gsm.19. The method according to claim 17, wherein, after exposing the glassstack configuration to the ceramming cycle, the glass sheet having theparting agent layer thereon has at least one of: a transmission metric(*T) of from about 19 to about 31; a transmission metric (*T) of fromabout 23 to about 27; a haze metric (*H) of from about 10 to about 50;or a haze metric (*H) of from about 20 to about
 40. 20. The methodaccording to claim 17, wherein, after exposing the glass stackconfiguration to the ceramming cycle, the glass sheet having the partingagent layer thereon has a surface layer effect of less than about 1micron.